You are given a sentence and a question in the input. The information provided in the sentence should be enough to answer the question. You're expected to write the correct answer. Do not use any facts other than those provided in the sentence.

Sentence: The beaver thanked both the bear and the wolf for trying out his new bridge and then started to build yet another bridge close to the first bridge. 
Question: what did the bear and wolf cross, and why did they turn back?
They crossed a bridge, and they turned back because they were merely testing the structural integrity of the bridge.